1. Field of the Invention
The present invention relates to indexing apparatuses and, more particularly, is directed to indexable apparatuses for selectively orienting objects such as workholding devices in precise predetermined positions.
2. Description of the Invention Background
A number of different apparatuses have been developed for indexing a variety of articles between manufacturing operations to increase the efficiency of the manufacturing process. For example, various types of indexing apparatuses are typically used to accurately present a workpiece in a predetermined orientation relative to the spindle of a machining device such as a milling machine or the like.
One type of indexing device is disclosed in U.S. Pat. No. 2,339,986 to Engert. The device in that patent comprises an indexable device for indexing a shaft into a variety of different machining orientations about a single axis. While this device can support a shaft in various orientations to enable, for example, keyways to be cut in different locations on the shaft, the device can only hold a single shaft at a time and is ill-suited for supporting non-cylindrical workpieces.
Another indexable device is disclosed in U.S. Pat. No. 3,020,998 to Webb. That device comprises a turntable adapted to be indexed by the cyclic operation of a ratchet and pawl mechanism. A plurality of vise-like workholders are supported on the table and are adapted to be indexed about an axis such that the workholders can be positioned in various orientations relative to metal bending or crimping apparatus. This device, however, can only support workpieces in a single planar orientation about the device's axis. Moreover, the ratchet and pawl system cannot be used to index the workholders to very precise angular orientations.
U.S. Pat. No. 2,369,425 to Becker discloses an indexable workholding device that comprises a frame that is adapted for attachment to the machining table of a machining device such as drill press. A disk is rotatably attached to the frame and may be rotated about an axis and secured in a predetermined position by clamping members attached to the frame. The top of the disk is also configured to accept workpiece holding clamps thereon. The outer edge of the disc is provided with a vernier scale that cooperates with an indicator on the frame to very precisely indicate the rotational position of the disc relative to the frame. The workpiece accuracy is dependent upon the secure clamping of the disk in position and the secure clamping of the workpiece on the disk. If either the workpiece or the disk moves even slightly, the workpiece accuracy will be compromised. A similar apparatus for retaining workpieces at selective angles is also disclosed in U.S. Pat. No. 2,406,043 to Sorensen. That device also comprises a rotatable plate member that is equipped with a plurality of threaded apertures adapted to receive workholding clamping members therein. Although this device is capable of indexing a workpiece at relatively precise angular orientations, if the clamping assemblies attaching the workpiece move, the workpiece accuracy is compromised.
U.S. Pat. No. 4,324,161 to Klancnik, et al. discloses an automatic turret lathe that includes a pneumatically indexable turret. The turret is rotated by an air operated rack and pinion arrangement. After rotating to a desired position, the turret is retained by a "curvic" coupling arrangement. However, if the turret is supporting a payload that is eccentrically mounted such that it applies a torque to the turret, such torque could cause the curvic coupling to slip during its disengagement.
Today, many machine tools are computer or numerically controlled which enables such tools to outproduce their manually operated counterparts. In an effort to reduce the time necessary to index a workpiece or a series of workpieces for presentation to the machine tool, pneumatically and hydraulically operated indexing devices, which can be automatically controlled by the machine tool control system, have been developed. Such systems enable the workpieces to be automatically indexed to various predetermined orientations consistent with successive machining operations. The locking forces generated by such devices, however, are dependent upon the constant supply of the pressurized fluid to the device. Thus, if the fluid pressure is accidentally lost or discontinued, those indexing apparatuses can become unlocked and expose their payloads to damage from inadvertent contact with the machine tool.
In addition, indexing apparatuses are often exposed to large torques generated when large machining forces are applied at considerable distances from the central axis of the indexing apparatus. For example, drilling a 22.2 mm (0.875") diameter hole in steel would require a thrust of about 10,000 N (2300 lbs.). This force, if applied 100 mm (3.9") from center, would apply 1000N-m (750 ft-lbs.) of torque to the indexing apparatus. Such forces can cause the indexing apparatus to inadvertently slip during a machining operation. Thus, large locking forces are desired for retaining the indexing device in a locked position during machining. However, because the locking forces generated by prior fluid-actuated indexing apparatuses are dependent upon the magnitude and maintenance of the pressurized fluid to the device, if there is an undetected leak in the fluid supply system, the locking forces can be compromised.
Also, prior fluid-actuated indexing apparatuses that are automatically controlled by the machine tool controller lack means for automatically confirming that the indexing apparatus is in a "zero" or "home" position prior to initiating the machining operations. Thus, the operator must inspect the position of the indexing apparatus prior to starting the machining process. If the indexing apparatus is not in a starting position and the machining operation is accidentally commenced, the workholding devices and/or the workpiece(s) could be damaged by the machine tool.
Thus, there is a need for a fluid-actuated indexing apparatus that remains in a locked position when the supply of pressurized fluid is accidentally interrupted or discontinued from the apparatus.
There is a further need for an indexing apparatus that has means for signaling the operator and/or the computerized system controlling the apparatus that the apparatus is in a starting position.
Another need exists for an indexing apparatus that has means for signaling when the apparatus is locked in position.
There is still another need for an indexing apparatus that can accurately index loads that are eccentrically mounted thereto.